3567 A.D. Mankind has lost its once-great civilisation, and it now lives in the remains of its devastation. Despite the fact that their lives are threatened by Gardeners, strange unmanned mobile weapons (of various levels) delivered from the Moon, daring youths must become Gardener hunters to make a livelihood. And, while human society as a whole is in ruins as a result of high-tech maintenance-free technology, some areas of the remaining cities continue to function in limited ways, supporting the humans who live there. Tokito Aizawa encounters Tea one fateful day, unleashing a power older and greater than that of the Gardeners and accidentally opening the door to a perhaps far brighter future for the rest of humanity...